DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Below, embodiments of the present invention will be explained with reference to the drawings.

[0041] First Embodiment

[0042] FIG. 1 is a view of the configuration of a wafer flattening system according to a first embodiment of the present invention.

[0043] The wafer flattening system is provided with a local etching device for locally etching the silicon wafer W and a smoothing device for smoothing the silicon wafer W after local etching.

[0044] Specifically, the wafer flattening system is provided with a plasma generator 1 serving as the first and second plasma generation units, an alumina discharge tube 2 serving as the first and second discharge tubes, a gas feed device 3 serving as the first and second gas feed units, an X-Y drive mechanism 4 serving as first and second X-Y drive units, and a Z-drive mechanism 4 .

[0045] The plasma generator 1 is a device for causing discharge of the gas in the alumina discharge tube 2 to generate a plasma and generate the first and second activated species gas and is comprised of a microwave generator 10 and waveguide tube 11 .

[0046] The microwave generator 10 is a magnetron and can generate a microwave M of a predetermined frequency.

[0047] The waveguide tube 11 propagates the microwave M generated from the microwave generator 10 and has a hole 12 through which the alumina discharge tube 2 is inserted.

[0048] The inside of the left end of the waveguide tube 11 is provided with a reflection plate (short plunger) 13 reflecting the microwave M to form a standing wave. Further, in the middle of the waveguide tube 11 are provided a 3-stub tuner 14 for phase alignment of the microwave M and an isolator 15 for bending the reflected microwave M heading toward the microwave generator 10 in the 90° direction (front surface direction of FIG. 1 ).

[0049] The alumina discharge tube 2 is a cylindrical body having a nozzle portion 20 at its lower end, the top end thereof is connected to a feed pipe 30 of the gas feed device 3 .

[0050] The gas feed device 3 is a device for feeding gas to the inside of the alumina discharge tube 2 . The gas feed device 3 has a bomb 31 for SF ₆ (sulfur hexafluoride) gas, a bomb 32 for O ₂ (oxygen) gas, and a bomb 33 for CF ₄ (carbon tetrafluoride) gas and these bombs 31 , 32 , and 33 are connected through a valve 37 and flow controllers 34 , 35 , 36 to the feed pipe 30 . Due to this, the SF ₆ gas bomb 31 , flow controller 34 , valve 37 , and feed pipe 30 constitute a first gas feed unit, while the O ₂ gas bomb 32 , CF ₄ gas bomb 33 , flow controllers 35 , 36 , valve 37 , and feed pipe 30 constitute a second gas feed unit.

[0051] Due to the plasma generator 1 having this configuration, when gas is fed from the gas feed device 3 to the alumina discharge tube 2 and a microwave M is generated from the microwave generator 10 , plasma discharge occurs at the location of the alumina discharge tube 2 corresponding to the hole 12 and the activated species gas generated by the plasma discharge is sprayed from the nozzle portion 20 .

[0052] The silicon wafer W is designed to be arranged above a chuck 7 in the chamber 6 . The chuck 7 has a mechanism for picking up a silicon wafer W by static electricity.

[0053] The chamber 6 is provided with a vacuum pump 60 . This vacuum pump 60 can be used to create a vacuum in the chamber 6 . Further, a hole 61 is formed in the center of the top surface of the chamber 6 . A nozzle portion 20 of the alumina discharge tube 2 is inserted into the chamber 6 through this hole 61 . An O-ring 62 is fit between the hole 61 and the alumina discharge tube 2 to hold the space between the hole 61 and the alumina discharge 2 air tight. The chamber 6 as a whole can be moved vertically relative to the alumina discharge tube 2 .

[0054] A duct 63 is provided around the nozzle portion 20 inserted in this hole 61 . By driving the vacuum pump 64 , it is possible to exhaust the reaction product gas to the outside of the chamber 6 at the time of etching.

[0055] The X-Y drive mechanism 4 is arranged inside this chamber 6 and supports the chuck 7 from below.

[0056] This X-Y drive mechanism 4 makes the chuck 7 move laterally in FIG. 1 by an X-drive motor 40 and makes the chuck 7 and the X-drive motor 40 move perpendicularly with respect to the surface of FIG. 1 together by a Y-drive motor 41 . That is, it is possible to make the nozzle portion 20 move relatively in the X-Y direction with respect to the silicon wafer W by the X-Y drive mechanism 4 .

[0057] The Z-drive mechanism 5 supports the X-Y drive mechanism 4 as a whole in the chamber 6 from the bottom. The Z-drive mechanism 5 makes the X-Y drive mechanism 4 as a whole move vertically by the Z-drive motor 90 to enable adjustment of the distance between the opening 20 a of the nozzle portion 20 and the front surface of the silicon wafer W.

[0058] The X-drive motor 40 and the Y-drive motor 41 of the X-Y drive mechanism 4 and the Z-drive motor 90 of the Z-drive mechanism 5 are controlled by a control computer 45 based on a predetermined program.

[0059] Next, an explanation will be made of the operation of the wafer flattening system of this embodiment. Note that the operation of the wafer flattening system specifically realizes the wafer flattening process of the present invention.

[0060] First, the wafer flattening system is operated to execute the local etching step.

[0061] That is, in the state with the silicon wafer W picked up by the chuck 7 , the vacuum pump 60 is driven to create a low atmospheric pressure state of 0.1 Torr to 5.0 Torr in the chamber 6 and the Z-drive mechanism 5 is driven to raise the X-Y drive mechanism 4 as a whole to bring the silicon wafer W to about 4 mm below the nozzle portion 20 .

[0062] In this state, the valve 37 of the gas feed device 3 is opened, the SF ₆ gas in the bomb 31 is made to flow out of the feed pipe 30 , and the SF ₆ gas is fed inside the alumina discharge tube 2 serving as the first discharge tube.

[0063] At this time, the opening degree of the valve 37 is adjusted to maintain the pressure of the SF ₆ gas at a predetermined pressure and the flow controller 34 is used to control the flow rate of the SF ₆ gas.

[0064] When the microwave generator 10 is driven in parallel with this feed operation of SF ₆ gas, the microwave M causes the SF ₆ gas present at the discharge location to discharge to generate a plasma and generate a first activated species gas G 1 containing F (fluorine) radicals. Due to this, the first activated species gas G 1 is guided into the nozzle portion 20 of the alumina discharge tube 2 and sprayed from the opening 20 a of the nozzle portion 20 to the silicon wafer W side.

[0065] In this state, the X-Y drive mechanism 4 is driven by the control computer 45 and the chuck 7 picking up the silicon wafer W is made to move in a zig-zag in the X-Y direction.

[0066] That is, as shown in FIG. 2 , the nozzle portion 20 is made to move in a zig-zag relative to the silicon wafer W. At this time, the relative speed of the nozzle portion 20 with respect to the silicon wafer W is set to be substantially inversely proportional to the thickness of the relatively thick portion.

[0067] Due to this, as shown in FIG. 3 , the nozzle portion 20 moves directly over the non relatively thick portion Wb at a high speed and when arriving above the relatively thick portion Wa is reduced in speed in accordance with the thickness of the relatively thick portion Wa. As a result, the etching time with respect to the relatively thick portion Wa becomes longer and the relatively thick portion Wa is shaved flat. By etching the entire front surface of the silicon wafer W in this way, the local etching step is completed.

[0068] This local etching step enables achievement of flattening of the front surface of the silicon wafer W, but there may be a slight roughness at the front surface of the silicon wafer W.

[0069] Therefore, the wafer flattening system is made to operate in the following manner to perform the smoothing step for the silicon wafer W after the local etching step.

[0070] That is, the X-Y drive mechanism 4 shown in FIG. 1 stops being driven, the valve 37 of the bomb 31 is closed, then the Z-drive mechanism 5 is driven to lower the entire X-Y drive mechanism 4 as a whole in the state holding the degree of vacuum in the chamber 6 etc. at the above conditions. Due to this, the silicon wafer W is moved away to about 250 mm below the nozzle portion 20 .

[0071] The valves 37 of the bombs 32 , 33 of the gas feed device 3 are opened in this state to allow O ₂ gas and CF ₄ gas to flow out to the feed pipe 30 and form a mixed gas (second mixed gas) to be supplied to the inside of the alumina discharge tube 2 as the second discharge tube.

[0072] At this time, the opening degrees of the valves 37 are adjusted to maintain the pressure of the O ₂ gas and CF ₄ gas at predetermined pressures and the flow controllers 35 , 36 are used to adjust the flow rates of the O ₂ gas and CF ₄ gas and set the ratio of the O ₂ gas with respect to the CF ₄ gas in the mixed gas fed to the alumina discharge tube 2 to a value between 200 and 400 percent.

[0073] When the microwave generator 10 is then driven and a microwave M used to make the mixed gas discharge and generate a plasma, a second activated species gas G 2 containing a larger amount of O radicals than F radicals is generated. Due to this, the second activated species gas G 2 is sprayed from the opening of the nozzle portion 20 of the alumina discharge tube 2 to the silicon wafer W side.

[0074] At this time, since the silicon wafer W is located away from the nozzle portion 20 of the alumina discharge tube 2 , as shown in FIG. 4 , the activated species gas G 2 sprayed from the nozzle portion 20 spreads downward and strikes the entire front surface of the silicon wafer W.

[0075] When the second activated species gas G 2 is blown on the front surface of the silicon wafer W, as shown in FIG. 5 , since O radicals are present, a reaction product S believed to be SiOxFy (x, y=1, 2, . . . ) is generated. Further, the F radicals etch the front surface of the silicon wafer W. Further, the reaction product S occurs at the entire front surface of this silicon wafer W, but the vapor pressure causes the majority of the reaction product S to evaporate and the reaction product S accumulated in the fine recesses Wc causing roughness to remain without being evaporated. Therefore, the reaction product S accumulates in the recesses Wc to protect the recesses from being etched by the F radicals, so only the portions other than the recesses Wc are etched by the F radicals.

[0076] Therefore, as shown by the broken line in FIG. 5 , when the surface of the reaction product S successively deposited in the recesses Wc becomes equal to the surface of the portions being etched, the plasma generator 1 stops being driven, the valves 37 of the bombs 32 , 33 are closed, and the second activated species gas G 2 stops being sprayed from the nozzle portion 20 .

[0077] Due to this, the smoothing step is ended and it is possible to obtain a silicon wafer W with a substantially completely flattened front surface.

[0078] In this way, according to the wafer flattening system of this embodiment, since it is possible to substantially completely eliminate the roughness of the front surface of the silicon wafer W caused by the local etching, it is possible to improve the RMS of the silicon wafer W.

[0079] To prove this point, the present inventors set the ratio of the O ₂ gas with respect to the CF ₄ gas in the mixed gas to 250 percent when performing the smoothing step and performed the local etching step and smoothing step on nine silicon wafers W under the same conditions as this embodiment, whereupon the results shown in FIG. 6 were obtained.

[0080] As shown in FIG. 6 , when nine silicon wafers W with initial RMS's of 0.3 nm, 0.1 nm, 0.4 nm, 0.8 nm, 0.3 nm, 0.6 nm, 0.4 nm, 0.2 nm, and 0.8 nm were flattened by the local etching step, the RMS's deteriorated to 1.0 nm, 0.9 nm, 2.2 nm, 3.3 nm, 2.5 nm, 2.9 nm, 2.6 nm, 0.9 nm, and 5.0 nm.

[0081] When the smoothing step was then further performed on the nine silicon wafers W, the RMS's of the nine silicon wafers W became 0.2 nm, 0.2 nm, 0.3 nm, 0.6 nm, 0.3 nm, 0.7 nm, 0.4 nm, 0.3 nm, and 0.5 nm.

[0082] That is, the result was obtained that it is possible to improve the RMS of the silicon wafer W to better than the initial value by flattening the silicon wafer W by the local etching step, then performing the smoothing step.

[0083] Note that depending on the state of roughness of the front surface of the silicon wafer W after the local etching step and the state of spraying of the second activated species gas G 2 , the second activated species gas G 2 may not be blown uniformly over the entire front surface of the silicon wafer W.

[0084] Therefore, as shown in FIG. 7 , by driving the X-Y drive mechanism 4 and making the silicon wafer W rotate on the center line L in the state with the center line L of the nozzle portion 20 and the center point O of the silicon wafer W aligned, it is possible to blow the second activated species gas G 2 uniformly over the entire front surface of the silicon wafer W.

[0085] Further, as shown in FIG. 8 , it is also possible to make the silicon wafer W revolve around the center line L in the state with the center line L of the nozzle portion 20 and the center point O of the silicon wafer W offset. In this case, it is possible to blow the second activated species gas G 2 uniformly by making the silicon wafer W rotate on the center point O.

[0086] Second Embodiment

[0087] FIG. 9 is a schematic cross-sectional view of a local etching device of a wafer flattening system according to a second embodiment of the present invention; and FIG. 10 is a schematic cross-sectional view of a smoothing device of this wafer flattening system. Note that the explanation is given by attaching the same reference numerals to members the same as those shown in FIG. 1 to FIG. 8 .

[0088] The wafer flattening system, as shown in FIG. 9 and FIG. 10 , differs from the wafer flattening system according to the first embodiment in the point that the local etching device for performing the local etching step and the smoothing device for performing the smoothing step are made separate.

[0089] The local etching device, as shown in FIG. 9 , is comprised of a plasma generator 1 serving as the first plasma generation unit, an alumina discharge tube 2 serving as the first discharge unit, a gas feed device 3 serving as the first gas feed unit, and an X-Y drive mechanism 4 serving as the first drive unit.

[0090] The gas feed device 3 is a device for feeding an SF ₆ gas to the inside of the alumina discharge tube 2 and has a SF ₆ gas bomb 31 connected to a feed pipe 30 through the feed controller 34 and valve 37 . These constitute the first gas feed unit.

[0091] Due to this configuration, when the flow rate of the SF ₆ gas is adjusted by the flow controller 34 to feed the SF ₆ gas inside the alumina discharge tube 2 and the microwave generator 10 of the plasma generator 1 is driven, the first activated species gas G 1 containing the F radicals is generated and sprayed from the opening of the nozzle portion 20 of the alumina discharge tube 2 to the silicon wafer W side.

[0092] By driving the X-Y drive mechanism 4 in state and making the chuck 7 picking up the silicon wafer W move zig-zag in the X-Y direction to locally etch the relative thick portions of the silicon wafer W, it is possible to perform the local etching step.

[0093] On the other hand, the smoothing device, as shown in FIG. 10 , is provided with a plasma generator 1 ′ serving as the second plasma generation unit, an alumina discharge tube 2 ′ serving as the second discharge tube, a gas feed device 3 ′ serving as the second gas feed unit, and a chuck 7 ′ affixed on a base 8 in the chamber 6 ′.

[0094] The alumina discharge tube 2 ′ is attached to the side surface of the chamber 6 ′ in the state with the nozzle portion 20 ′ inserted in the chamber 6 ′.

[0095] The gas feed device 3 ′ is a device for feeding a mixed gas of the above O ₂ gas and CF ₄ gas (second mixed gas) inside the alumina discharge tube 2 ′ and has an O ₂ gas bomb 32 and CF ₄ gas bomb 33 connected through the flow controllers 35 , 36 and valves 37 to the feed pipe 30 . These constitute the second gas feed unit.

[0096] Due to this configuration, when a mixed gas adjusted to a ratio of the O ₂ gas with respect to the CF ₄ gas of a value between 200 to 400 percent by the flow controllers 35 , 36 is fed to the alumina discharge tube 2 ′ and the microwave generator 10 of the plasma generator 1 ′ is driven, the second activated species gas G 2 containing a larger amount of O radicals than F radicals is generated and the second activated species gas G 2 is filled in the chamber 6 ′ from the opening of the nozzle portion 20 of the alumina discharge tube 2 ′.

[0097] In this state, when the silicon wafer W flattened by the local etching step of the local etching device is conveyed to the inside of the chamber 6 ′ filled with the second activated species gas G 2 and placed on the chuck 7 ′ and the entire surface of the silicon wafer W is exposed to the second activated species gas G 2 for a predetermined period, the roughness of the front surface of the silicon wafer W is smoothed by the same action as that shown in FIG. 5 and thereby the smoothing step can be performed.

[0098] In this way, the wafer flattening system of this embodiment is configured to be able to perform the local etching step and the smoothing step separately by a separate local etching device and smoothing device. Therefore, there is no need to make the next silicon wafer stand by until the completion of the smoothing step of a prior silicon wafer as in the wafer flattening system of the first embodiment and as a result it is possible to raise the throughput of the silicon wafer W processing.

[0099] The rest of the configuration and the mode of operation and advantageous effects are similar to those of the first embodiment explained above, so explanations thereof will be omitted.

[0100] Note that the present invention is not limited to the above embodiments. Various modifications and changes may be made within the scope of the gist of the invention.

[0101] For example, in the above embodiment, as the fluorine compound of the first gas feed unit, SF ₆ gas was used, but it is also possible to use CF ₄ gas or NF ₃ (nitrogen trifluoride gas). Further, while the first feed unit to the alumina discharge tube 2 are configured to feed solely SF ₆ gas, but it is also possible to configure them to feed a mixed gas of SF ₆ gas and O ₂ gas and other gas (first mixed gas) to the alumina discharge tube 2 .

[0102] Further, as the mechanism for making the nozzle portion 29 move relative to the silicon wafer W, an X-Y drive mechanism 4 was used, but it is also possible to use an r-θ drive mechanism for making the nozzle portion 20 move relative to the radial direction and center angle direction of the nozzle portion 20 .

[0103] Further, in the above embodiment, as the first and second plasma generation units, use was made of the plasma generator 1 for generating a microwave to generate plasma, but any means able to generate an activated species gas may be used. For example, of course it is possible to use a plasma generator which generates a plasma using a high frequency to generate an activated species gas and various other types of plasma generators.

[0104] As explained above in detail, according to the present invention, since the first activated species gas is used to flatten the front surface of the wafer, then the second activated species gas is used to smooth the surface of the wafer, it is possible to remarkably reduce the surface roughness of the wafer and as a result there is the superior effect of providing a high quality wafer.